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From:   Logan Gunthorpe <logang@deltatee.com>
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Date:   Tue, 8 May 2018 13:13:40 -0600
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Subject: Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all devices
 behind switches
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On 08/05/18 10:50 AM, Christian König wrote:
> E.g. transactions are initially send to the root complex for 
> translation, that's for sure. But at least for AMD GPUs the root complex 
> answers with the translated address which is then cached in the device.
> 
> So further transactions for the same address range then go directly to 
> the destination.

Sounds like you are referring to Address Translation Services (ATS).
This is quite separate from ACS and, to my knowledge, isn't widely
supported by switch hardware.

Logan